How do you snap a solid steel, 10-inch-diameter, shaft and what does it cost?

May. 17, 2013

Everyone is looking to save a buck. When you run a rock crusher repair shop like we do, you see a lot of consequences of these cost-cutting schemes. Let’s say that you tried to save some money in the pit by widening your shot pattern a few inches. That worked so well that you widened them a bit more and a bit more until your shot-rock can barely make it into the primary crusher. Never mind, for the moment, that your pit loader is now struggling with digging toe and laying out oversize, and that the vast rows of oversize gets in the way of pit development, and the coarse shot is beating the daylights out of your truck beds—let’s just look at what ends up in our shop.

The picture you see here is the result of giving a jaw crusher too coarse a feed. The over-sized rocks start crushing too high up in the chamber, where they push against the pitman barrel and cause the pitman shaft to flex. Eventually the shaft becomes weakened and starts cracking. If you look closely at the picture you can see the lines where the shaft broke, little by little.

Our recommendation is that you don’t fill the crushing chamber any higher than manufacturer’s recommendation. You’ll want enough material to get rock-on-rock action and keep pushing material down through the discharge opening, but you don’t want material to ride any higher because you’ll start to get problems like the one you see here.

Too coarse a feed probably also means you are going to see bridging and you’ll have to find a safe way of clearing the upper end of the crushing chamber, which usually means buying a very expensive hydraulic breaker…which operators like to use as extra weight to push bridging material through the jaw…which causes a break-up of the structure that the breaker sits on.

While we welcome the business of repairing pitmans and selling hydraulic breakers, we would rather see our customers minimize their cost-per-ton and use their savings to grow their operations. Keeping your pitman from snapping is one way improving your margins and avoid repairing machines prematurely.

So what does a repair like this cost? Depends on if you include your cost of lost production and any penalties for unfulfilled contracts and fixed costs for equipment that suddenly sits idle. We’re not saying that widening your shot pattern is a bad thing; just saying that when you hit on a money-saving idea, take a moment and consider possible consequences, or give us a call and we can advise on possible pros and cons of your idea.

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